Apparatus for linearizing saw-tooth waves



June 14, 194. M, J, ARSEN 2,473,208

APPARATUS FOR LINEARIZING SAW-TOOTH WAVES Filed Nov. -14, 1944 "Yl/A/L/I/v V V V V VW?? E MT5 BY eS/l l/ l/ l/ l/ l/ 1 A wrok/Vey Patented June 14, 1949 2,473,208 APPARATUS FOR LINEARIZING SAW-TOOTH WAVES Merwin J. Larsen,

Rochester, N. Y., assignor to Stromberg-Carlson Com a corporation of New York pany, Rochester, N. Y.,

Application November 14, 1944, Serial No. 563,388

(Cl. Z50-36) 2 Claims. 1

This invention relates to a method of and to apparatus for generating saw-tooth waves.

A common method for generating saw-tooth voltage waves employs a circuit having a capacitor, a suitable resistor and a constant potential source connected in series therein. The capacitor is charged to a fraction of the value of the supply potential and then discharged abruptly through a low resistance discharge path periodically completed across the terminals of the capacitor. This method aiords a reasonable approach to linearity between charging voltage and time, if the capacitor is allowed to charge to only a small fraction of the supply voltage. However, in order to utilize the resulting saw-tooth voltage, perhaps by amplication, it is often necessary to connect a load resistor across the mentioned capacitor. This connection further reduces the charging current as the capacitor Voltage rises.

One feature of the present invention relates to a method of linearizing a saw-tooth wave.

Another feature of the invention relates to apparatus for producing a constant charging current in the charging capacitor included in a conventional Saw-tooth generator.

An additional feature of the invention relates to a method of introducing into a saw-tooth generator network, an additional current by positive feed back action which additional current compensates for that lost in the charging circuit of the conventional capacitor.

A further feature of the invention relates to amethod of and to apparatus for providing a linearized saw-tooth wave with a larger voltage than can be derived from conventional generators.

Other features and advantages will appear from the detailed description and claims when taken with the drawings in which:

Fig. 1 is a diagrammatic showing of a saw-tooth generator constructed in accordance with the present invention and by which the method of the present invention may be practised; and

Fig. 2 is a chart showing certain wave forms useful in describing the apparatus.

In the present arrangement, as in conventional saw-tooth generators, there is provided a capacitor 5 which is arranged to be charged through the resistor 6, with current supplied through the potentiometer 1, from a positive supply 8. The use of potentiometer 1 permits adjustment of the amplitude of the voltage applied to the capacitor 5. The capacitor 5 is periodically discharged through the electron discharge tube 9 such as a present method and ,j

pentode tube having the characteristics of a tube now sold under the code number 6SJ7. The input circuit of this tube which is connected to the cathode I0 and grid Il includes the resistor I5. An input voltage, having repetitive strong positive peaks, as indicated at I6, is supplied across the resistor l5. The mentioned input voltage I5 may be generated by any well known means, such as a blocking oscillator (not shown). This peak voltage is of such value that it causes the tube 9 to conduct and thereby to discharge the capacitor 5 rapidly through conductor Il and across the space between the anode I t and cathode Il) of this tube, to ground. After the capacitor has thus discharged to a fairly low value, the tube 9 is biased to cut-oit by the mentioned input voltage, now of reduced value, so that no current flows in the plate circuit of tube 9 and the mentioned discharge path of capacitor 5, is interrupted. A load circuit comprising a capacitor I8 and resistors I9 and 20, is connected to the conductor I'l and one terminal of the capacitor 5 so that the desired saw-tooth voltage wave form e1, resulting from the alternately recurring charge and discharge of capacitor 5, can be taken ofi at the terminal 2|.

The charging current i2 decreases in value as the capacitor 5 becomes charged and this charging current is further decreased by the current is, the amount depending on the load. Such decreasing charging current tends to render the resulting saw-tooth voltage wave non-linear. In accordance with the present invention, there is provided a novel method and novel apparatus for supplying by means of positive feed-back control action, a supplemental current which compensates for the mentioned decreasing charging current so that a substantially constant charging current is supplied to the capacitor 5. The positive feedback arrangement is shown in the lower part of Fig. 1, whereby a portion of the voltage e1 present across resistors I9 and 20, activates triode 22 which is connected as a conventional phase inverter. Thus, a saw-tooth voltage wave e2 similar to e1 but of opposite phase with respect thereto can be taken oi at terminal 26. By proper adjustment of the divider resistors i9 and 2G, the voitage e2 at terminal 26 can be made to have the same amplitude as voltage e1 but of opposite phase because of the phase inversion. Voltages e1 and e2 can be ampliiied in a suitable amplier 4i! and can then be used to effect magnetic or electrostatic deection in connection with a cathode ray tube deflection system 4i.

A portion of the voltage e2 present across potenof the reactances of capacitors I8, 34 and 32 be very low as compared with` their associated resistors I9, 20, 21 and 33 respectively.

If the input or the triode 3| is properly adjusted by means of the potentiometer 21, the current i4 can be easily adjusted to compensate for variations in the charging current ii, so that the charging current is constant during the charging period. A predetermined amount of over or under compensation is also possible in this arrangement, in case either is desired.

While triodes 22 and 3| have been disclosed it should be understood that they may be replaced by a single twin-triode tube such as is now sold under the code number BSN?.

Fig. zshows the voltage wave form er and the four currents involved in the charging of capacitor 5, the Wave forms being shown under conditions of proper compensation. be noted that the current i2 becomes smaller as the potential across capacitor 5 increases because the difference across resistance 6 decreases. The current i3 further decreases the charging current, the amount depending upon the load. T

It is necessary that the compensating current i4 supply the deficiency of i2 and i3. Neglecting tube distortion inv triodes 22 and 3|, the voltage wave on theplate 30 of triode 3| is the same in shape as e1 except for the amplitude. Hence, a saw-tooth current i4 can be supplied which compensates for the drop produced by that from i2 and i3 alone. Under normal conditions, Where the compensating current i4 need not be excessive, the distortion in the triodes 22 and 3| would have a very minor effect because the compensating current itself is small, From the foregoing, it may be stated that the algebraic sum of the primary current (i2) plus the load current (is) and the compensating current (i4) is a constant and consequently produces a Charging voltage across capacitor 5 which is proportional to a constant times time.

To show the order of magnitudes involved, an example will be given. Assume that capacitor 5 varies from 20 to 50 volts, then with a supply source of 250 volts and with suitable circuit parameters, i2 will vary, for example, from 460 to 400 microamperes. is varies approximately from +20 to 20 micrcamperes. The current i4 must supply, therefore, a total peak to peak value of It should I 60+40 or lomicroamperes and in the proper phase. This means a peak to peak voltage on the plate 3|) of triode 3| of 22 vo1ts+30 (22 in excess of the capacitor swing) or 52 volts. This voltage can be supplied from a tube such as a 6SN7 with negligible distortion insofar as the overall effect is concerned.

By this corrective means', in addition to linearity control, a much larger voltage swing is permissible betwen the outputs 2| and 26 than would otherwise be possible.

What I claim is:

1. In a saw-tooth voltage wave generator, a capacitor, a load circuit coupled to said capacitor, means including a source of electrical energy for charging said capacitor, means including a periodically completed discharge path for clischarging said capacitor, means for supplying a separate compensating charging current to said capacitor, a phase inverter unit responsive to a voltage developed in said load circuit', and a thermionic unit responsive-to at least a portion of the output voltage of said inverter unit for controlling the supplying of said compensating current to said capacitor in such a manner that the sum of the charging currents is substantially constant.

2. In a saw-tooth voltage wavev generator, a capacitor, a load circuit coupled to said-capacitor, means for charging said capacitorincluding a source of direct current potential and a resistance connected in series relationship with said capacitor, means including a periodically completed discharge path for discharging said capacitor, and means for supplying a compensating charging current to said capacitor of such value that the sum of the charging currents is substantially constant, said compensating .means comprising a phase inverter unit responsive to a voltage developed in said load circuit and a thermionic unit responsive to at least a portion o-theoutput voltage of said inverter unit, theoutput circuit of said thermionic unit being connected to-saidcapacitor in parallel relationship with said charging means.

MERWINy J; LARSEN.

REFERENCES CITEDn The following references are ofy record in the rile of this patent:

UNITED STATES PATENTS Number Name Date 2,037,577 Harries Apr.,1419 36 2,126,243 Busse et al Aug. v9, 1938 2,153,217 Mark Apr. 4, 1939 2,195,996 Palmer Apr. 2, 1940 2,232,076 Newsam Feb. 18 1941 2,237,425 Geigeret al. Apr. 8, 1941 2,412,063 Rosentreter Dec. 3, 1946 2,419,606 Stodola Apr. 29,1947 

